1. Technical Field
This invention relates to an airfoil having improved lift coefficients at operational angles of attack and more specifically the present invention relates to an airfoil having upper camber portions that may be positioned to form a single upper camber portion or several upper camber portions.
2. Description of the Prior Art
The primary concern with any airfoil design is twofold; first to produce a greater amount of lift without adversely increasing drag and second to enable the airfol to function at greater angles of attack without stalling. With respect to the wing of an airplane for example, a design suitable for producing substantial lift at low air speeds inherently produces excessive drag at high air speeds and on the other hand a wing designed to fly with minimal drag at high air speeds generally fails to produce sufficient lift at low air speeds to maintain flight as during take-offs and landings. This latter condition results in the stalling of the wing as the angle of attack of the wing is increased in an effort to produce greater lift until the critical angle of attack is exceeded. It is understood that an airfoil will stall at any air speed whenever the angle of attack of the airfoil to the free stream air flow exceeds a critical angle of attack for the particular air foil. The prior art includes movable slots and/or flaps on the lead and trailing edges of the wing which change the cross sectional profile of the wing. The slots and/or flaps may be adjusted during flight for optimum performance of the wing at various flight conditions. At high air speeds the slots and/or flaps are fully retracted to give the wing a relatively thin streamlined profile reducing the drag acting thereon. At lower air speeds the slots and/or flaps are extended downward to produce a greater camber on the wing which permits the wing to develop greater lift along with greater drag. The use of slots and/or flaps thus increase the aircraft's operational angles of attack through which the aircraft can safely operate, but because of the increase in drag the extension of the slots and/or flaps is only advisable at relatively low air speeds and thus they are unable to improve the lift and stall characteristics of the wing at high cruising air speeds.
The present invention provides an airfoil with means of altering the upper surfaces thereof so as to optionally form a relatively thin streamlined profile having a single continuously extending upper surface forming a positive upper camber portion and alternately forming a first upper surface extending rearwardly from the leading edge defining a positive upper camber portion and a second upper surface rearwardly of said first upper surface and defining a second variable upper camber portion.